1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by using a perpendicular magnetic recording system and to a method of manufacturing such a magnetic head.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared to the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically used have a layered structure comprising a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing. The write head comprises magnetic poles that produce a magnetic field in the direction orthogonal to the surface of the recording medium.
For the perpendicular magnetic recording system it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in writing characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the writing characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, are reduced. It is therefore required to achieve better writing characteristics as the track width is reduced.
A magnetic head used for a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has a medium facing surface that faces toward a recording medium. This medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider slightly flies over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt called a skew of the magnetic head is created with respect to the tangent of the circular track, in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system that exhibits a better capability of writing on a recording medium than the longitudinal magnetic recording system, in particular, if the above-mentioned skew is created, problems arise, such as a phenomenon in which data stored on an adjacent track is erased when data is written on a specific track (that is hereinafter called adjacent track erasing) or unwanted writing is performed on adjacent two tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing on adjacent two tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
A technique is known for preventing the problems resulting from the skew as described above, as disclosed in the Published U.S. Patent Application No. 2003/0151850 A1, the Published Unexamined Japanese Patent Application 2003-203311, and the U.S. Pat. No. 6,504,675 B1, for example. According to this technique, the end face of the pole located in the medium facing surface is made to have a shape of trapezoid in which the side located backward in the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is smaller than the other side.
As a magnetic head for perpendicular magnetic recording, a magnetic head comprising a magnetic pole and a shield is known, as disclosed in the U.S. Pat. No. 4,656,546, for example. In this magnetic head an end of the shield is located forward of an end of the pole along the direction of travel of the recording medium with a specific small space. Such a magnetic head will be hereinafter called a shield-type head. In the shield-type head the shield prevents a magnetic flux from reaching the recording medium, the flux being generated from the end of the pole and extending in directions except the direction orthogonal to the surface of the recording medium. The shield-type head achieves a further improvement in linear recording density.
The U.S. Pat. No. 4,672,493 discloses a magnetic head having a structure in which magnetic layers are provided forward and backward, respectively, in the direction of travel of the recording medium with respect to a middle magnetic layer to be the pole, and coils are disposed between the middle magnetic layer and the forward magnetic layer, and between the middle magnetic layer and the backward magnetic layer, respectively. This magnetic head is capable of increasing components orthogonal to the surface of the recording medium among components of the magnetic field generated from the medium-facing-surface-side end of the middle magnetic layer.
Reference is now made to FIG. 17 to describe a basic configuration of the shield-type head. FIG. 17 is a cross-sectional view of the main part of an example of the shield-type head. The shield-type head comprises: a medium facing surface 100 that faces toward a recording medium; a coil 101 for generating a field corresponding to data to be written on the medium; a pole layer 102 having an end located in the medium facing surface 100, allowing a magnetic flux corresponding to the field generated by the coil 101 to pass, and generating a write magnetic field for writing the data on the medium by means of the perpendicular magnetic recording system; a shield layer 103 having an end located in the medium facing surface 100 and having a portion located away from the medium facing surface 100 and coupled to the pole layer 102; a gap layer 104 provided between the pole layer 102 and the shield layer 103; and an insulating layer 105 covering the coil 101.
In the medium facing surface 100, the end of the shield layer 103 is located forward of the end of the pole layer 102 along the direction T of travel of the recording medium with a specific space created by the thickness of the gap layer 104. At least part of the coil 101 is disposed between the pole layer 102 and the shield layer 103 and insulated from the pole layer 102 and the shield layer 103. The end of the pole layer 102 located in the medium facing surface 100 has a shape of trapezoid in which the side closer to the gap layer 104 is longer than the other side.
The coil 101 is made of a conductive material such as copper. The pole layer 102 and the shield layer 103 are made of a magnetic material. The gap layer 104 is made of an insulating material such as alumina (Al2O3). The insulating layer 105 is made of photoresist, for example.
In the head of FIG. 17 the gap layer 104 is disposed on the pole layer 102 and the coil 101 is disposed on the gap layer 104. The coil 101 is covered with the insulating layer 105. One of the ends of the insulating layer 105 closer to the medium facing surface 100 is located at a distance from the medium facing surface 100. In the region from the medium facing surface 100 to the end of the insulating layer. 105 closer to the medium facing surface 100, the shield layer 103 faces toward the pole layer 102 with the gap layer 104 disposed in between. Throat height TH is the length (height) of the portions of the pole layer 102 and the shield layer 103 facing toward each other with the gap layer 104 disposed in between, the length being taken from the end closer to the medium facing surface 100 to the other end. Throat height TH affects the intensity and distribution of the field generated from the pole layer 102 in the medium facing surface 100.
In the shield-type head as shown in FIG. 17, for example, it is preferred to reduce throat height TH to improve the overwrite property. It is required that throat height TH be 0.1 to 0.3 micrometer (μm), for example. When such a small throat height TH is required, the following two problems arise in the head of FIG. 17.
The first problem of the head of FIG. 17 is that it is difficult to define the throat height TH with accuracy. That is, typically, the throat height TH is controlled by the depth to which the medium facing surface 100 is polished. When the medium facing surface 100 is polished, forces are applied to the portion of the shield layer 103 located between the insulating layer 105 and the medium facing surface 100: the force from the medium facing surface 100 to the insulating layer 105 and the force from the insulating layer 105 to the medium facing surface 100. In addition, the volume of the insulating layer 105 is much greater than the volume of the portion of the shield layer 103 located between the insulating layer 105 and the medium facing surface 100. Furthermore, the photoresist constituting the insulating layer 105 is relatively soft. Because of these factors, when the medium facing surface 100 is polished, the portion of the shield layer 103 located between the insulating layer 105 and the medium facing surface 100 varies, particularly when the throat height TH is small. As a result, variations of throat heights TH obtained after the medium facing surface 100 is polished occur.
The second problem of the head of FIG. 17 is that, when the head is operated, the end of the shield layer 103 located closer to the medium facing surface 100 is likely to protrude, which results from the heat generated by the coil 101. The reasons follow. The volume of the insulating layer 105 is much greater than the volume of the portion of the shield layer 103 located between the insulating layer 105 and the medium facing surface 100. Furthermore, the photoresist constituting the insulating layer 105 has a relatively high thermal expansion coefficient. Because of these factors, in the head of FIG. 17, the volume of expansion of the insulating layer 105 due to the heat generated by the coil 101 increases. As a result, the end of the shield layer 103 closer to the medium facing surface 100 is likely to protrude. This protrusion of the end of the shield layer 103 induces collision of the slider with the recording medium.